This invention relates to sewing machines and, more particularly, to sewing machines having stitch forming instrumentalities operatively controllable by supplying power to position respective electromechanical actuators.
Sewing machines are known in the prior art wherein the positional coordinates for successive stitch penetrations are stored in a memory having addressable locations corresponding to a plurality of operator selectable patterns. In particular, a system is disclosed in U.S. Pat. No. 4,016,821, issued on Apr. 12, 1977, wherein logic circuitry is used to select and release the stitch pattern information stored in the memory in timed relation with the operation of the sewing machine. Digital information from the memory is converted to positional analog signals which control closed loop servo systems including moving coil linear actuators directly controlling the position of conventional stitch forming instrumentalities of the sewing machine to reproduce a pattern of stitches corresponding to the selected stitch information. Another system is disclosed in U.S. Pat. No. 3,847,100, issued Nov. 12, 1974, wherein a solenoid is utilized as an actuator for a skip stitch mechanism effective to suspend needle reciprocation. In both of these prior systems, the actuators operate independently fom the main drive motor of the sewing machine. Under certain abnormal operating conditions, undesirably high power may be applied to the actuators although the main drive motor is not operating and stitches are not being formed. During such time, due to the relatively high continuous current applied to the actuators, the actuators are subject to overheating and further, the interior of the sewing machine casing experiences a rise in temperature. It is therefore an object of the present invention to reduce operating temperatures and heat dissipation of the sewing machine actuators when the sewing machine main drive motor is not operating.
One way of accomplishing the foregoing object would be to remove power from the actuators when the sewing machine main drive motor is not operating. However, this is not a desirable approach because, for example, the actuator controlling the lateral position of the needle should maintain its position so as to resist the needle being moved in the process of changing or threading it. It is therefore another object of this invetion to reduce the operating temperatures and heat dissipation of the sewing machine actuators when the sewing machine main drive motor is not operating without entirely removing power therefrom.
It is a further object of this invention that the sewing machine operator not be aware of any such power limitation if the sewing machine is operating normally.